WASHINGTON — The threat by majority Democrats to change Senate rules to make confirmation easier for some nominees could open up two cans of worms that could weaken the chamber's minority party for years to come.

Exasperated by what he considers excessive Republican efforts to block some of President Barack Obama's appointments, Senate Majority Leader Harry Reid, D-Nev., is threatening to use his muscle to change the rules so only simple majority votes are needed to approve top-level federal agency jobs.